This invention relates to a seat belt device adapted for use in automotive vehicles, and more particularly to a device of this kind which has an improved buckle-supporting structure which imparts enhances the initial restrainability of the occupant in the event of a collision of the vehicle.
Seat belt devices of a three-point type are generally used at a driver's seat, an assistant driver's seat, etc. in automotive vehicles. The three-point type seat belt device has a safety belt which first upwardly extends from a retractor anchored to a lower portion of a pillar of the vehicle body close to a door and then downwardly turned back by a guide member mounted on an upper portion of the pillar, with one end thereof fixed to an anchor plate mounted on a lower portion of the pillar. An intermediate portion of the safety belt is pulled by the occupant and releasably retained by a buckle arranged at a central lateral side of a seat. The buckle is supported by the vehicle body through a linkage to assure positive restraint of the occupant in the event of a collision of the vehicle, etc. In the case where the seat is adjustable in vertical position, the buckle is preferably vertically movable to follow the adjusted vertical position of the seat, to permit the safety belt to be easily mated with the buckle and released therefrom. To this end, various buckle-supporting structures have so far been developed. For example, such a buckle-supporting structure has been proposed by Japanese Provisional Patent Publication (Kokai) No. 63-32951, which employs a flexible linkage.
FIG. 1 shows an example of conventional seat belt device to which a linkage is applied. A buckle 4 is arranged at a central or inner lateral side of a vertically-adjustable cushioned seat 1 and supported by a flexible linkage 5, to receive a tongue plate 3 fitted on a safety belt 2, which is releasably inserted into the buckle 4.
The linkage 5 comprises a first stay 7 having one end thereof pivoted to a fulcrum shaft 6 fixed to a vehicle body for pivotal movement thereabout, and a second stay 10 having one end thereof engaged, through an engaging pin 8 and a through hole 9, with the other end of the first stay 7, for movement in vertical directions, as shown by the arrow a, as well as for pivotal movement back and forth, as shown by the arrow b. The buckle 4 is secured to the other end of the second stay 10.
With such arrangement, whenever the cushioned seat 1 is vertically adjusted, the buckle 4 moves vertically through pivotal motion of the first and second stays 7, 10, to thereby follow the adjusted vertical position of the seat 1.
However, according to the conventional device described above, the through hole 9 is elongate along the direction of extension of the linkage 5, to obtain a large stroke of extension and contraction of the linkage 5. As a consequence, when a tension load is applied to the belt 2 in the event of an impact upon the device, such as a collision of the vehicle, the linkage 5 is extended into such a position that the first and second stays 7, 10 form a straight line, as shown by the two-dot-chain lines in FIG. 1.
During extension of the linkage 5, the belt 2 is ineffective to restrain the occupant. As a consequence, when the vehicle undergoes a collision, the timing of starting restraint of the occupant is retarded to increase the inertial motion amount of the occupant, thereby making it difficult to positively protect the occupant, particularly his head, from being accelerated.